Manufacture and production of artificial threads, filaments, and the like by the viscose process



Patented Feb. 27,,

UNITED STATES PATE - 2,192,074 OFFICE \MANUFACTURE AND PRODUCTION OF ARTI- FICIAL THREADS,

FIIAMENT S,ANDTHE LIKE BY THE VISCOSE PROCESS British company No Drawing. Application November 27, 1936, Se rial No. 113,072. In Great Britain December 6 Claims.

In the production of viscose threads, the viscose, after being forced through holes in a jet, was originally and is even now sometimes drawn directly on to a collecting bobbin, or passed over one positively driven roller 'into acentrifugal spinning box. The pull of the collecting bobbin or'of the positively driven roller drawsthethread away from the jet, but the tension so applied is used up in pulling the liquid viscose away from the jet before it is solidified to a thread and if the thread does not touch any other surface before arriving at the winding bobbin, there is little or no stretching of the coagulated or partially coagulated part of the thread.

In the early days of the viscose artificial silk industry, however, it was shown that by applying a stretch to that part of the thread which is partiallycoagulated and still plastic, it was possible to increase the strength of the thread. Thus, Ernst (U, S. specification No. 808,148) in 1905 subjected different portions of the length of the thread between the spool and the perforated cap to different degrees of tension to apply a definite predetermined stretch to the filaments between the bath and the winding-spool. Ernst carried out his process by passing the thread round glass rods.

Borzykowski (British specification No. 149,295 of 1920) also applied, stretch to the partially coagulated and still plastic thread by passing it round a roller rotating at a certain speed and then collecting it on a roller rotating at a greater peripheral speed. By way of example, he states that the plastic thread may bev stretched 25 per cent.

It has recently been suggested that the increase in strength of the thread, caused by stretching it whilst it is in a partially coagulated and still plastic condition, is due to the fact that the tension applied to the thread causes the cellulose micelles to take up to a greater or lesser extent a position parallel to the length of the filament. Various processes for the production of strong threads from viscose have been described, which utilise the principle of stretching the thread while it is still in a partially coagulated and plastic condition. Thus, Lilienfeld in British specification No. 274,521 projects viscose through a jet into a-bath of strong sulphuric acid, and then applies additional stretch to the thread, either in the coagulating bath or between the coagulating bath and the collecting device, or in both places.

Again, in his'British specification No. 298,548, Lilienield states that he can produce threads of high tenacity from viscose by employing one agent as the coagulant and another for producing the plasticising or swelling action, while the thread may be stretched eitherin the coagulating bath or subsequently. In this case, all setting baths known from the viscose art may be used as coagulants, and this would include, for instance, a bath of from 2.5 to per cent sulphuric acid, as described by Borzykowski in British specification No. 116,268.

W. Harrison, British specification No. 309,053, describes coagulating viscose filaments in strong or mineral acids of hydrogen ion concentration less than that of 7 per cent H2804 (for instance, a bath containing 2.5 per cent sulphuric acid) in such a manner as to cause the viscose to pass through a nascent or active plastic or active colloidal state and applying tension with gradually increasing stress to the filaments while in that state, whereby the filaments are extended at least 25 per cent or more. As a modification of his process he passes the coagulated filaments immediately or very soon after their formation, into a-solution in which a swelling of the filaments takes place, and stretches the filaments before complete decomposition of the viscose.

The I. G. Farbenindustrie, British specification No. 340,138, describes the stretching of freshly precipitated viscose thread by, means of heated rollers, at the same time applying to the rollers washing liquids, such as water, salt solutions, acids, alkalies or the like, such solutions having previously been raised to the'temperature of the heated rollers.

British specification No. 335,605, Zellstoff- Fabrik Waldhof,describes a non-continuous process of producing artificial threads from viscose, inwhich the thread, after precipitation and fixing, is led directly through a hot water bath and then immediately spooled. The specification furstates that if the threadbe subjected to strong tension while passing through the hot water bath, the strength of the threads is considerably increased.

We have now found that if viscose filaments be first coagulated in a dilute acid bath containing sulphuric acid .and also sufficient metallic sulphate to delay the decomposition to cellulose hydrate, and if the incompletely-decomposed filaments, after they have left the coagulating bath, be stretched in the presence of hot dilute acid, filaments of relatively high tenacity can be obtained. The metallic sulphate which we prefer to employ is zinc sulphate, say 2.5 per cent or preferably 4 per cent ZnSO4, in addition to a quantity, for example of from 15 to 24 per cent of sodium sulphate.

The incompletely decomposed filaments may be subjected to the action of hot dilute acid, for example by passing them through a bath containing dilute sulphuric acid, for example 1.5 per cent mm at 95 centigrade, or the filaments acid coagulating bath taken over by the filaments. The stretch may be applied to the filaments by passing them round two rollers revolving at different speeds, care being taken-to avoid slipping of the filaments on the rollers. The stretching of the filaments according to this invention must be carried out at a temperature of at least centigrade and we prefer to employ a temperature of 80 centigrade or higher.

After the filaments have been stretched in the presence of hot dilute acid as aforesaid, they can be subjected to the action of hot or cold water, during which, if desired, the stretching can be continued.

The process of this invention is particularly applicable to the production of continuous filaments from viscose by the centrifugal process, and also to the production of discontinuous filaments such as staple fibre, for instance when the filaments, after leaving the coagulating bath and passing through the hot dilute acid bath in which stretching is effected, are passed into a cutter of the type described in British specification No. 289,028.

The following example will further illustrate the nature of this invention, but the invention is not limited to this example. The parts are by weight.

Example Viscose containing 7.4 per cent of cellulose is passed through a nozzle containing 60 holes, at such a rate that the finished thread is about 120 denier, into a bath containing 9.5 per cent of sulphuric acid, 4.0 per cent of zinc sulphate and 20 per cent of sodium sulphate, at a temperature of 50 centigrade, the coagulated filaments being allowed to remainin the bath for a distance of about 20 centimetres. The thread is then immediately led round a wheel with a peripheral speed of 30 metres per minute and then for a distance of, 50 centimetres through a bath containing 1.5 per cent of sulphuric acid with the addition of 3 percent of sodium sulphate and 0.4 per cent of zinc sulphate, at 95 centigrade, then round a second wheel rotating with a peripheral speed of 56 metres per minute and it is collected finally in a centrifugal box rotating at 6,000 revolutions per minute.

By our invention we are able to obtain threads with a wet tenacity of about 2.0 grams per denier.

What we claim is:

1. A process for the manufacture and production of continuous or discontinuous filaments of relatively high tenacity from Viscose which consists in partially coagulating the viscose filaments in a bath containing sulphuric acid and zinc and sodium sulphates wherein the proportion of the salts to the acid is such that immediate complete coagulation is prevented, then stretching the thus coagulated filaments with attendant reduction in cross section while passing them -i through a dilute acid bath which contains less acidthan the aforesaid coagulating bath and is maintained at atemperature above 60. centigrade, which increases the plasticity of the partially decomposed cellulose xanthate filaments.

2. A process for the manufacture and production of continuous or discontinuous filaments of relatively high tenacity from viscose which consists in partially coagulating the viscose filaments in a bath containing sulphuric acid and zinc and sodium sulphates wherein the proportion of the salts to the acid is such that immediate complete coagulation is prevented, then stretching the thus coagulated filaments with attendant reduction in cross section while'passing them through a dilute acid bath which contains less acid than the aforesaid coagulating bath and is maintained at a temperature above 60 centigrade, which increases the plasticity of the partially decomposed cellulose xanthate filaments, acid for said dilute acid bath being the filaments from the coagulating bath.

3. A process for the manufacture and produc tion of continuous or discontinuous filaments of relatively high tenacity from viscose which consists in partially coagulating the viscose filaments provided by acid taken over by in a bath containing sulphuric acid and sodium sulphate and at least 2.5 per cent of zinc sulphate, the proportion of the said salts to the acid being such that immediate complete coagulation is prevented, then stretching the thus coagulated filaments with attendant reduction in cross section while passing them through a dilute acid bath which contains less acid than the aforesaid coagulating bath and is maintained at a temperature above 60 centigrade, which increases the filaments with attendant reduction in cross section while passing them through a dilute acid bath which contains less acid than the aforesaid coagulating bath and is maintained at a temperature above 60 centigrade, which increases the plasticity of the partially decomposed cellulose xanthate filaments.

5. A process for the manufacture and production of continuous or discontinuous filaments of relatively high tenacity from viscose which consists in partially coagulating the viscose filaments in a bath containing about 9.5 per cent of sulphuric acid, 4.0 per cent of zinc sulphate and 20 per cent of sodium sulphate, the said proportions of salts to acid being such that immediate complete coagulation is prevented, then stretching the thus coagulated filaments with attendant reduction in cross section by leading them in succession round two rollers, the second of which is rotating with a peripheral speed about 87 per cent greater than that of the first, while passing them through a dilute acid bath which contains less acid than the aforesaid coagulating bath and is maintained at a temperature of about centigrade which increases the plasticity of the partially decomposed cellulose xanthate filaments.

6. Process as claimed in claim 2 in which the proportion of zinc sulphate is at least 2.5% and the proportion of sodium sulphate is between 15% and 24%, and in which the filaments are subjected to the action of a hot gaseous fluid which heats up the said acid taken over by the filaments from the coagulating bath. JOHN HARRISON GIVENS.

HUGH WATSON BlDDULPH. LESLIE ROSE. 

